FIG. 7 is a cross-sectional view showing a surface emitting laser disclosed in "Room Temperature Pulsed Oscillation of GaAlAs/GaAs Surface Emitting Junction Laser Grown by MBE" by K. Iga, T. Nishimura, K. Yagi, T. Yamaguchi, and T. Niina, Japanese Journal of Applied Physics, Vol.25 (1986), pp.924-925.
In FIG. 7, reference numeral 30 designates a (100) oriented n type GaAs substrate. An n type GaAs layer 31 is disposed on a main surface of the substrate 30. An n type Al.sub.0.3 Ga.sub.0.7 As cladding layer 32 is disposed beneath the n type GaAs layer 31. A p type GaAs active layer 33 is disposed beneath the n type cladding layer 32. A p type Al.sub.0.3 Ga.sub.0.7 As cladding layer 34 is disposed beneath the active layer 33. A groove 43 of generally circular cross-section penetrates the substrate 30 and the n type GaAs layer 31. The p type cladding layer 34 has a circular mesa projection at a region opposite to the mesa groove 43. A p type Al.sub.0.1 Ga.sub.0.9 As layer 42 is disposed beneath the circular mesa projection of the p type cladding layer 34. A SiO.sub.2 film 35 is disposed beneath the p type cladding layer 34 covering the side surface and the circumference of the top surface of the circular mesa projection. A circular SiO.sub.2 high reflectivity film 36 is disposed at the center of the top surface of the circular mesa projection. A Au/Zn/Au electrode 45 covers the lowest part of the laser device and is connected to the ring-shaped surface 41 of the p type Al.sub.0.1 Ga.sub.0.9 As layer 42. A SiO.sub.2 film 37 is disposed on the other main surface of the substrate 30. A Au/Sn electrode 38 is disposed on the SiO.sub.2 film 37 and on the side surface of the groove 43. A Au mirror 44 is disposed on the bottom of the groove 43. An active region 39 is formed in a region in the active layer 33 just under the groove 43. Laser light 40 is emitted from the bottom of the groove 43 on which the Au mirror is disposed.
The operating principle of this surface emitting laser will be described. Electrons and holes supplied from the electrodes 38 and 45 are injected into the active layer 33. These electrons and holes are efficiently confined in the active layer 33 by the cladding layers 32 and 34 and combine to generate light having a wave-length equivalent to the energy band gap of the active layer 33. The generated light increases with an increase in the current level and is reflected and amplified between the Au mirror 44 on the bottom of the groove 43 and the circular SiO.sub.2 film 36 on the top surface of the circular mesa projection. When the current exceeds a certain value (threshold current), the gain exceeds the loss, generating a laser oscillation. Thus, the laser light 40 is emitted from the bottom of the groove 43.
In a case where the prior art surface emitting laser is formed using AlGaInP system materials, of course the surface emitting laser structure can be realized, but the current confinement in the active layer is not sufficient in the prior art structure. In addition, since the AlGaInP system materials have a higher thermal resistance than that of the AlGaAs series materials, it is difficult to generate a laser oscillation and even if a laser oscillation is generated, the temperature characteristic is very poor. In order to confine the current, a structure is generally employed in which only the active region (light emitting region) is left in a column shape by etching and the side surface of the active region is buried by an AlGaInP system material having a high resistance or by a pn junction. In this case, regrowth on AlGaInP containing Al which is easily oxidized is difficult. In addition, when an AlGaInP system material is regrown on a substrate having a step, there arises a problem such that an abnormal growth is induced by a remarkable difference in growth speed depending on the surface orientation.